If the screen resolution on your computer changes when you start Firefox, making everything appear big or distorted, you likely have Window's "Run in 640 x 480 screen resolution" feature activated on your Firefox shortcut. To turn off this feature:
- From the menu at the top of the Firefox window, select and then select the menu item.
- Right-click on the icon you use to start Firefox and choose .
- Open the tab.
- Uncheck Run in 640 x 480 screen resolution. You may have also see that Compatibility mode and Run in 256 colors are selected. These can also cause problems with Firefox and you should uncheck them.
- Click .
Now, when Firefox starts, your screen resolution should not change.